Automatic restricted service telephone system



Dec. 6, 1949 c. E. LOMAX AUTOMATIC RESTRICTED SERVICE TELEPHONE SYSTEM 4 Sheets-Sheet 2 Filed Jan. 5, 1947 5N E. 5% moml/ 5 s; x E5 3 158 E L 52 7 v ,II 82 0am M8 8 3 on 206 mhosmm 0mm ma 22 mam 0mm um m 8 Nai aw 3 50 x 5. oom xzsE. m azooww 88 memo N 01 ES /4 wowu Inventor Clarence E. Lomog Dec. 6, 1949 C, E. LO MAX AUTOMATIC RESTRICTED SERVICE TELEPHONE SYSTEM Filed Jan. 3, 1947 4 Sheets-Sheet 3 wmm mwm 2 1 m5 gmhr E n NNm mmm as: 6 #IIIIIIL \E 8 0% Y EM 8m 5550 x755 Inventor Clarence E. Lomox Attorneys Patented Dec. 6, 1949 AUTOMATIC RESTRICTED- SERVICE TELEPHONE SYSTEM Clarence E. Lomax, Chicago, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago 111., a corporation of Delaware Application January 3, 1947, Serial No. 720,078

The present invention relates to automatic telephone systems and moreparticularly to such systems in which different groups of subscriber substations are rendered corresponding different classes of service.

In an automatic telephone system serving a central office area and the adjacent suburban areas, calls from the subscriber substations in the central ofiice area that are to be completed to subscriber substations in the suburban areas are usually first extended to an operator switchboard in the central oifice area and then routed by the operators thereat to the subscriber substations in the suburban areas. While this'system is entirely satisfactory in operation, a large switchboard in the central office, staffed by a great number of operators is required in order to complete the calls from the central ofiice area to the suburban areas.

Accordingly, it is an object of the present invention to provide an automatic telephone system comprising an improved switching arrangement; whereby subscriber substations arranged in a first group in the central office are rendered a first class of service permitting them to set up connections for any desired time interval to subscriber substations in the suburban areas, subscriber substations arranged in a second group in the central office are rendered a second class of service permitting them to set up connections for a limited time interval to subscriber substations in the suburban areas, and subscriber substations arranged in a third group in the central oflice are rendered a third class of service preventing them from setting up connections to subscriber substations in the suburban areas.

Another object of the invention is to provide an automatic telephone system in which different classes of service are rendered to subscriber lines; wherein the classes of service are selectively established by an improved arrangement incorporated in the finders of the system.

Another object of the invention is to provide an automatic telephone system of the type noted; wherein the class of service rendered to a subscriber line is determined jointly by the operation of the finder to find the subscriber line and by the operation of subsequent switching apparatus to extend the connection from the finder.

A further object of the invention is to provide in a finder, characterized by different primary operations to select corresponding different groups of lines and by different secondary op;

eratlons to select corresponding different individual lines in the previously selected group of 5 Claims. (01. 179 1s) service.

'lines, an improved arrangement selectively controlled by different primary operations of the finder for establishing corresponding different classes of service tobe rendered to the lines in the different groups of lines selected by the finder.

A still further object of the invention is to provide in a finder of the type noted, an improved arrangement selectively controlled by different primary operations thereof for establishing first corresponding controls of classes of service to be rendered to the lines in the difierent groups of linesand selectively controlled by the particular secondary operations thereof for establishing corresponding second and overriding controls of classes of service to be rendered to the lines in the different groups of lines.

Further features of the invention pertain to the particular arrangement of the circuit elements of the system whereby the above outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects'and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which Figures 1 to 4, inclusive, taken together illustrate the details of an automatic telephone system having incorporated therein the features of the present invention. More particularly, Figs. 1 and 2 should be arranged from left to right in end-to-end relation; Figs. 3 and 4 should be arranged from left to right in endto-end relation; and Fig. 3 should be arranged above Fig. 2 in order to form a unified diagram.

Referring now, more particularly, to Figs. 1 to 4, inclusive, of the drawings, there is illustrated an automatic telephone system compris ing a central office [0, a different exchange 20 and a remote exchange 30. The central office lli'is co-nnected'to the distant exchange 20 by a group of ten trunk lines, including the trunk line 399;,and the central ofiice I0 is connected to the remote exchange 30 by a group of seven trunk lines, including the trunk line 232.

Thecentral office In may serve a group of several hundred subscriber substations rendered three individual classes of service, including nonrestricted service, limited service and restricted A first group of subscriber substations, including the subscriber substation A is rendered non-restricted service, a second group of subscriber substations, including the subscriber substation B, is rendered limited service; and a third group of subscriber substations, including the subscriber substation C, is rendered restricted service. Each subscriber substation is provided with conventional subscriber substation apparatus and is connected by an associated subscriber line to a line circuit individual thereto and associated with switching apparatus. The subscriber substation A is connected by the associated subscriber line 40 to the line circuit 4| individual thereto; the subscriber substation B is connected by the associated subscriber line 50 to the line circuit 5! individual thereto; and the subscriber substation C is connected by the associated subscriber line 60 to the line circuit 6| individual thereto. Further, the central office l0 comprises a plurality of groups of links each serving a group of 100 of the subscriber lines; the first group of links, including the link I00, serves the first group of .100 subscriber lines, including the subscriber lines 40, 50 and 60 respectively extending to the subscriber substations A, B and C. More particularly, the subscriber line 40 extending to the subscriber substation A is included in a first ten-line group within the first I00-line group; the subscriber line 50 extending to the subscriber substation B is included in a second ten-line group within the first I00-line group; and the subscriber line 60 extending to the subscriber substation C is included in a third ten-line group within the first I00-line group. The first group of links, including a link I00 is provided with a distributor 10 individual thereto; and each link comprises a finder and a selector, the link I00 comprising the finder FIDO and the selector Sl00. Also, the central office [0 comprises a plurality of groups of connectors, not shown, accessible to the selectors in the groups and utilized for the purpose of setting up local telephone connections. The first group of connectors, not shown, has access to the first I00-line group including the subscriber lines40, 50 and 60 respectively extending to the subscriber substations A, B and C.

Also, the central office l0 comprises a group of trunk circuits terminating the trunk lines in the group extending to the distant exchange 20; the trunk circuit 300 terminating the trunk line 390; and another group of trunk circuits terminating the trunk lines in the group extending to the remote exchange 30, the trunk circuit 281 terminating the trunk line 282; and a toll switchboard 295. The toll switchboard 295 terminates a group of three trunks, including the trunk 292, terminated by a further group of trunk circuits, including the trunk circuit 29!, the trunk 292 being terminated by the trunk circuit 29L Also, the central ofiice I0 comprises a group of, secondary trunks, including the secondary trunk 200. Each of the trunk circuits in the group, including the trunk circuit 300, is provided with an incoming trunk accessible to the selectors of the links in the difierent groups; the trunk circuit 300 being provided with the incoming trunk 2l0 accessible to the selector Sl00 of the link I00 in the first group. Each of the secondary trunks in the group, including the secondary trunk 200, is provided with an incoming trunk accessible to the selectors of the links in the difierent groups; the secondary trunk 200 being provided with the incoming trunk 205 accessible to the selector Sl00 of the link I00 in the first group. Each of the trunk circuits in the group, including the trunk circuit 28L is provided with an income ing trunk accessible to the hunt switches in corporated in the secondary trunks 200, etc.; the

, subscriber substations rendered two individual classes of service, including non-restricted service and limited service. A first group of subscriber substations,'including the subscriber substation D, is rendered non-restricted service; and asecond group of subscriber substations, including the subscriber substations E and F, are rendered limited service. Each subscriber substation is provided with conventional subscriber substation apparatus and is connected by an associated subscriber line to a line circuit individual thereto and associated with switching apparatus. The subscriber substation D is connected by the associated subscriber line 410 to the line circuit 4' individual thereto; the subscriber substation E is connected by the associated subscriber line 475 to the line circuit 416 individual thereto; and the subscriber substation F is connected by the associated subscriber line 480 to the line circuit 48! individual thereto. Further, the distant exchange 20 comprises a group of links, including the link 400, serving the subscriber lines mentioned, and provided with a distributor 490. More particularly, the subscriber lines 410 and 480 respectively extending to the subscriber substations D and F are included in a first ten-line group within the I00-line group; and the subscriber line 415 extending to the subscriber substation E is included in a second ten-line group within the -line group. At this point it is noted that while the subscriber line 480 extending to the subscriber substation F is included in the first ten-line group that is normally rendered non-restricted service, that this particular subscriber line is rendered limited service by virtue of the application of direct ground potential upon the EC conductor thereof in the contact banks of the finders of the associated links, as explained more fully hereinafter. Each of the links comprises a finder and a connector, the link 400 comprising the finder F400 and the connector C400. The connectors C400, etc., of the links 400, etc., have access to the subscriber lines mentioned. Also, the distant exchange 20 comprises a group of incoming connectors, including the incoming connector 465, terminating the group of trunk lines, including the trunk line 398; the incoming connector 465 terminating the trunk line 390. The incoming connectors 465, etc., have access to the subscriber lines 410, 415 and 480 respectively extending to the subscriber substations D, E and F.

The remote exchange 30 is of the automatic type, comprising conventional apparatus, and

renders any desired classes of service to a plurality of subscriber substations therein, not shown.

Preferably, in the central ofiice l0 each of the links is identical to the link I00 which comprises the finder Fl 00 and the selector S l 90. The finder F100 is of the Strowger type, comprising a relay group, not shown, and a Strowger mechanism l8! including a wiper carriage supporting three wipers I82, I83 and I84 and provided with an associated contact bank I85. Also, the Strowger mechanism I81 comprises a set of normal post switch springs SI86 which is selectively actuated in response to predetermined operations of the wiper carriage shaft I81 in the vertical direction. More particularly, when the wiper carriage of the Strowger mechanism I8I is operated one step in the vertical direction to select the first tenline group, including the subscriber line 40 extending to the subscriber substation A, rendered non-restricted service, the set of switch springs Slat is actuated to close the associated contacts I89, thereby to connect ground potential by way of the resistor I to the EC conductor CI04; when the wiper carriage of the Strowger mechanism I8I is operated two steps in the vertical direction to select the second ten-line group, including the subscriber line 50 extending to the subscriber substation B, rendered limited service, the set of switch springs SI86 is actuated to close the associated contacts, thereby to place no potential upon the EC conductor CI04; and when the wiper carriage of the Strowger mechanism I8I is operated three steps in the vertical direction to select the third ten-linegroup, including the subscriber line 60 extending to the subscriber substation C, rendered restricted service, the set of switch springs SI86 is actuated to close the associated contacts I88, thereby to connect direct ground potential to the EC conductor CI04. Accordingly, when the finder FI00 is operated to select a ten-line group rendered nonrestricted service, resistance ground potential is applied to the EC conductor Cl04; when the finder FI00 is operated to select a ten-line group rendered limited service, no potential is applied to the EC conductor CI04; and when the finder FI00 is operated to select a ten-line group rendered restricted service, direct ground potential is applied to the EC conductor CI04.

The selector SI00 is of the Strowger type and comprises a relay group including a test relay RI I0, a switch relay RI20, a line relay RI30, a hold relay RI40 and a transfer relay RI50; as well as a Strowger mechanism I60. The Strowger mechanism I60 comprises a wiper carriage supporting four wipers IGI, I02, I63. and. I04 provided with an associated contact bank; as Well as a vertical magnet MI 65, a rotary magnet MI 66 and a release magnet MI68. Associated with the wiper carriage of the Strowger mechanism I60 are three sets of switch springs SI69, SI10 and SI1I which are actuated when the wiper carriage is driven in the vertical direction away from its home position; as well as a set of normal the wiper carriage of the Strowger mechanism I60 is driven either one step or two steps in the vertical direction away from its home position and respectively corresponding to the group of trunks, including the trunk 205 and to the group of trunks, including the trunk 2I0. In other words, when the Strowger mechanism I60 is operated to select either the group of trunks, including the trunk 205, or the group of trunks, including the trunk 2 I 0, the set of switch springs SI12 is actuated.

Preferably, each of the secondary trunks is identical to the secondary trunk 200, which comprises a relay group including an answer relay R2 I0, a time release relay R220, a line relay R230, a test relay R240, a timer cutoif relay R250 and an intercept relay R260; as well as a timer 2I5 and a hunt switch 210. The hunt switch 210 is ofthe rotary type including four Wipers 211 to 6. 214, inclusive, provided with individually associated contact banks, and a magnet M215 for driving the wipers noted step by step in the clockwise direction.

Preferably, each of the trunk circuits is identical to the trunkcircuit 300, which comprises a relay group including a reverse battery relay R3 I 0, a timer cutoff relay R320, a release relay R330, a time release relay R340, a hold relay R350, a line relay R360 and an answer relay R310; as well as a repeater 380 and a timer 385.

Preferably, in the distant exchange 20 each of the links is identical to the link 400 which comprises the finder F400 and the connector C400. The finder F400 is of the Strowger type comprising a relaygroup including a switch-through relay R4I0, a service relay R420, an answer relay R430 and a'time. relay R450; as well as a Strowger mechanism 48I and a timer switch 440. The Strowger mechanism 48 I comprising a wiper carriage supporting four wipers 482, 483, 484 and 485 provided with an. associated contact bank 486; as well as vertical, rotary and release magnets, -not shown. Associated with the Strowger mechanism '48I is a set of switch springs, not shown, which is' actuated when the wiper carriage isdriven in the vertical direction away from its home position; as well as a set of normal post switch springs S481, which is selectively operated in response to predetermined operations of the wiper carriageshaft 488 in the vertical direction. More particularly, when the wiper carriage of the Strowger mechanism 48I is operated one step in the vertical direction to select the first tenline group, including the subscriber lines did and 480 respectively extending to the subscriber substations D and F, respectively rendered non-restricted service and limited service, the set of switch'springs S481 is actuated to close the associated contacts, thereby to connect no potential to the EC conductor; and when the wiper carriage of the Strowger mechanism 48I is operated two steps in the vertical direction to select the second ten-line group, including the subscriber line 415extendin'g to the subscriber substation E, rendered limited service, the set of switch springs S481 is actuated to close the associated contacts 489, thereby to connect direct ground potential to the associated EC conductor. Accordingly, when-the finder F400 is operated to select a tenline group rendered non-restricted service, no ground potential is applied by the set of switch springs S481 to the associated EC conductor; and when the finder F400 is operated to select a ten- 5 line group rendered limited service, direct ground post switch springs -SI12, which 18 actuated when potential is applied by the set of switch springs $481 to the associated EC conductor. Notwithstanding operation of the finder F400 to select a ten-line group rendered non-restricted service, direct ground potential may be applied to the associated EC conductor via the wiper 405 incident to complete operation of the finder F400 to select a particular line in the ten-line group mentioned; which particular line in the selected ten-line group is rendered limited service. This is brought about by the application of direct ground potential to the EC contact in the contact bank 480 engaged by the wiper 485 of the Strowger mechanism 48! in response to operation thereof to select the particular line in the previously selected ten-line group.

The timer switch 440 incorporated in the finder F400 is of the minor type comprising a wiper 44! provided with an associated contact bank, a magnet M442 for' driving the wiper noted step by step 7. in the clockwise direction and a release magnet M443 for releasing the wiper noted and for causing it to be returned to its normal home position. Also, associated with the wiper I is a set of switch springs S444 which is actuated when the wiper noted is driven away from its home position.

The connector C400 is of the Strowger type and comprises a conventional relay group, not shown; as well as a Strowger mechanism, the wiper set of which is diagrammatically illustrated.

Operation of the finders in the central office 10 First, assuming that a call is initiated at a subscriber substation, such, for example, as the subscriber substation A in the tenline group rendered non-restricted service in the central ofiice II]; the line circuit 4| is controlled over the associated subscriber line 40 and operates in order to place ground potential upon the start conductor 01 I' extending to the distributor I and to mark the particular rotary position of the contact sets terminating the subscriber line 40 in the contact banks of the Strowger mechanisms incorporated in the finders of the links in the first group. The distributor I0 then operates in order to assign an idle one of the links in the first group to find the calling line, such, for example, as the link I08. Also, the distributor marks to the finder FIN of the link ID'I'I the level of the contact set in the contact bank I85 of the Strowger mechanism I8I terminating the calling subscriber line 40'; the first level in the present example. The finder FIUD is then controlled by.

the distributor Ill; whereby the wiper carriage of the Strowger mechanism IBI is driven one step in the vertical direction and then operated automatically in the rotary direction in search of the calling subscriber line 40.

When the wiper set of the Strowger mechanism I8! engages the third contact set in the first level in the contact bank I85 terminating the calling subscriber line 40, further operation thereof is arrested; the distributor I0 is released; and the line circuit 4| associated with the calling subscriber line 40 is controlled in order to mark the subscriber line 40 as busy to the connectors in the associated group having access thereto. Also, at this time, a loop circuit is completed including the wipers I82 and I83, the line conductors CIDI and. CIOZ, and the contacts I2I and I23 for energizing in series the upper and lower windings of the line relay RIB!) in the selector S I 00; whereby the latter relay operates. Upon operating the line relay RI completes, at the contacts I3I, a circuit, including the contacts III and I25, for operating the hold relay RI'4IJ. Upon operating the hold relay RI40 completes, at the contacts I43, an obvious path for applying ground potential to the control conductor CI03, and consequently to the wiper I84, thereby to maintain the line circuit 4! associated with the subscriber line 40 in its operated position as previously noted. Also, the hold relay RI4Ilcompletes, at the contacts I43, a circuit, including the set of switch springs SITB, for energizing the lower winding of the transfer relay RIEI), thereby to cause the latter relay to operate. At this time, the selector SIlIO is conditioned to be responsive to the first digit dialed at the calling subscriber substation A, since the previously traced loop circuit is completed between the calling subscriber substation A and the line relay RI3Il in the selector S100.

Also, incident to operation of the finder FIM 8 to find the calling line 40, the wiper carriage shaft I81 actuates the set of switch springs SI86 to close the contacts I89; whereby ground potential is applied by way of the resistor I90 to the EC conductor CI04 extending into the selector SIDD; by virtue of the fact that the calling subscriber line 40 is terminated in the first level of the contact bank I85 of the Strowger mechanism I8I. This application of resistance ground potential -to the EC conductor CI04 extending into the selector SIOU establishes a control which may be utilized ultimately in the switch train beyond the selector SIIl'I], in the event the subscriber at the calling substation A operates the selector S I 00 in order to make a trunk call to the distant exchange 20 or to the remote exchange 30, as explained more fully hereinafter.

Now assuming that a call is initiated at a subscriber substation, such, for example, as the subscriber substation B in the ten-line group rendered limited service in the central oifice ID; the line circuit 5| is controlled over the associated subscriber line 50 and operates in order to place ground potential upon the start conductor CII extending to the distributor "I9 and to mark the particular rotary position of the contact sets terminating the subscriber line 50 in the contact banks of the Strowger mechanisms incorporated inthe finders of the links in the first group. The distributor Ill then operates in order to assign an idle one of the links in the first group to find the calling line, such, for example, as the link I00. Also, the distributor 10 marks to the finder FIDO of the link I00 the level of the contact set in the contact bank I85 of the Strowger mechanism I 8| terminating the calling subscriber line 59; the second level in the present example. The finder FIDO is then controlled by the distributor I0; whereby the wiper carriage of the Strowger 4n mechanism is driven two steps in the vertical direction and then operated automatically in the rotary direction in search of the calling subscriber line 50.

When the wiper set of the Strowger mechanism :I8I engages the second contact set in the second level in the contact bank I85 terminating the calling subscriber line 40, further operation thereof is arrested; the distributor I0 is released; and the line circuit 5| associated with the calling subsgnscriber line is controlled in order to mark the subscriber line 59 as busy to the connectors in the associated group having access thereto. Also, at this time, a loop circuit is completed in order to effect operation of the line relay RI30, the hold relay RIM] and the transfer relay RI50 in the selector I00 in the manner previously explained; whereby the selector SIOIJ is conditioned to be responsive to the first digit dialed at the calling subscriber substation B, since the loop circuit .mentioned is completed between the calling subconductor CI04 extending into the selector SIIJO;

by virtue of the fact that the calling subscriber line 58 is terminated in the second level of the contact bank I85 of the Strowger mechanism I8I. This application of no potential to the EC conductor C104 extending into the selector SI 00 establishes a control which may be utilized ultimately in the switch train beyond the selector I 9 SI00, in the event the subscriber at the calling subscriber substation B operates the selector SI in order to make a trunk call to the distant exchange or to the remote exchange 30, as explained more fully hereinafter.

Finally, assuming that a call is initiated at a subscriber substation, such, for example, as the subscriber substation C in the ten-line group rendered restricted service in the central oflice I0; the line circiut BI is controlled over the associated subscriber line 60 and operates in order to place ground potential upon the start conductor C'II extending to the distributor I0 and to mark the particular rotary position of the contact sets terminating the'subscriber line 60 in the contact banks of the Strowger mechanisms incorporated in the finders of the links of the first group. The distributor I0 then operates in order to assign an idle one of the links in the first group to find the calling line, such, for example, as the link I00. Also, the distributor marks to the finder FI00 of the link I00 the level of the contact set in the contact bank I85 of the Strowger mechanism I8I terminating the calling subscriber line 60; the third level in the present example. The finder FI00 is then controlled by the distributor I0; whereby the wiper carriage of the Strowger mechanism I8I is driven three steps in the vertical direction and then operated automatically in the rotary direction in serach of the calling subscriber line 60. I

When the wiper set of the Strowger mechanism I 8I engages the tenth contact set in the third level in the contact bank I 85 terminating the calling subscriber line 60, furtheroperation thereof is arrested; the distributor I0 is released; and the line circuit 6| associated with the calling subscriber line 00 is controlled in order to mark the subscriber line 60 as busy to the connectors in the associated group having access thereto. Also, at this time, a loop circuit is completed in order to efiect operationof the line relay RI30, the hold relay RI 40 and the transfer relay RI50 in the selector SI00 in the manner previously explained; whereby the selector SI00 is conditioned to be responsive to the first digit dialed'at the calling subscriber'substation C, since the loop circuit mentioned is completed between the calling subscriber substation C and the line relay RI30 in the selector SI00.

Also, incident to operation of the finder F|00 to find the calling subscriber line 60, the wiper carriage shaft I81 actuates the set of switch springs SIBS to close the associated contacts I88;

whereby direct ground potential is applied to the EC conductor CI04 extending into the selector SHED; by virtue of the fact that the calling subscriber line 60 is terminated in the third level of the contact bank I85 of the Strowger mechanism I8I. This application of direct ground potential to the EC conductor CI04 extending into the selector S I 00 establishes a control which may be utilized ultimately in the switch train beyond the selector SI00, in the event the subscriber at the calling subscriber substation C operates the selector SI00 in order to attempt to make a trunk call to the distant exchange 20 or to the remote exchange 30, as explained more fully hereinafter.

Local calls in the central oflice 10 Now assume that a call has been initiated at any subscriber substation in the central office I 0-, such, for example, as the subscriber substation A; that the finder FI00 of the link I00 has operated to seize the calling'subscriber line 40;"and that the selector SI 00 of the link I00 is conditioned to be responsive to the first digit dialed at the calling subscriber substation A. When the subscriber. at the callingsubscriber substation A dials the first digit the line relay RI30 in the selector SI00 follows the impulses thereof. Each time the line relay RI30 restores and then reoperates, it interrupts and then recompletes, at the contacts I3I, the previously traced circuit for maintaining operated the hold relay RIM, the latter relay remaining operated during the digit since it is of the slow-to-release type; and completes and then interrupts, at the contacts I32, a multiple circuit, including the contacts II I, I and MI,

, for energizing the upper winding of the transfer relay RISE] andthe vertical magnet MI65. The transfer relay RI50 being of the slow-to-release type remains operated during the digit; and the vertical magnet MI65 is operated a number of times corresponding to the number of impulses of the first digit dialed. at the calling subscriber substation A. When the wiper carriage of the Strowger mechanism I60 is driven away from its home position the sets of switch springs SI69, SIM and SI'II are actuated. lVIore particularly, the set of switch springs SII0 is actuated into disengagement thereby to interrupt the previously traced circuit for energizing the lower winding of the transfer relay RI50; however, the latter relay is maintained in its operated position, at this time, by virtue of the intermittent completion of the previously traced circuit for energizing the upper winding thereof, since the transfer relay RI 50 is of the slow-to-release type.

At the conclusion of the first digit the line relay RI is maintained in its operated position in order to maintain operated the hold relay RI40; whereby the transfer relay RI restores shortly thereafter. At this time, the wiper carriage of the Strowger mechanism I is operated in the vertical direction to select a group of trunks extending to the corresponding group of connectors, not shown; whereby the set of switch springs SI I2 is not actuated. As previously noted, the

. set of switch springs .SI'IZ is actuated only when the wiper carriage of the Strowger mechanism I60 is driven either one step or two steps away from its home position in order. to select respectively the two groups of trunks including the trunks 205 and 2I0; which positions the wiper carriage of the Strowger mechanism I60 does not occupy at this time, since the first digit dialed at the calling subscriber substation A was the first digit of a directory number corresponding to a local call. Thus, the application of resistance ground potential in thefinder FIBI) upon the EC conductor CIII I extending into the selector SI00 is without effect and will not be utilized ultimately, since the set of switch springs SI'IZ was not actuated in the present example in response to movement of the wiper carriage of the Strowger mechanism I60 in the vertical direction. Upon restoring the transfer relay RI50 completes, at the contacts I5I, a circuit, including the contacts III, I25 and I3I, the set of switch springs SI'II and the contacts I5I and I61, for operating the rotary magnet MI66. Upon operating the rotary magnet MIB6 interrupts, at the contacts I61, the previously traced operating circuit therefor; whereby the rotary magnet MI66 operates buzzer-fashion in order to drive the wiper carriage of theStrowger mechanism I60 step by step in the rotary direction.

When the wiper carriageof the Strowger mechanism I60 is driven one step in the rotary direc- 11 tion, the first trunk in the previously selected group, not shown, extendin'g'to the correspond.- ing connector in the associated group, not shown, is tested; battery potential appearing upon the control conductor thereof in the event the connector mentioned is idle and ground potential appearing upon the control conductor thereof in the event the connector mentioned is busy. The application of ground potential to the control conductor of the selected trunk completes a path, including the control wiper I63 and the contacts I", for short-circuiting the winding of the test relay RI III; whereas the application of battery potential to the control conductor of the trunk mentioned completes an identical circuit for energizing the winding of the test relay RI I0, thereby to cause the latter relay to operate. Accordingly, the rotary magnet MIBB efiects automatic operation of the Strowger mechanism I60 in the rotary direction until an idle trunk ex- 20 tending to an idle connector in the associated group, not shown, is selected in conformity with conventional practice; whereupon the test relay RIIII operates. Upon operating the test relay RIIII interrupts, at the contacts III, the previously traced multiple circuits for maintaining operated the hold relay RHO and for operating the rotary magnet MISS; whereby the hold relay RIM] restores shortly thereafter, it being of the slow-to-release type, and further operation of the rotary magnet MISS is positively prevented. Also, upon operating the test relay RI IIl completes, at the contacts II 2, an obvious circuit for operating the switch relay RIZIJ; whereby the latter relay interrupts, at the contacts IZI and I23, the previously traced loop circuit extending between the calling subscriber substation A and the upper and lower windings of the line relay RIM, causing the latter relay to restore. Also, the switch relay RI20 completes, at the contacts I26, a holding circuit, including the contacts I63, for energizing the winding thereof and completes, at the contacts I22 and I 24, a further loop circuit extending from the calling subscriber substation A and, including the line wipers I8I and I82, to the connector, not shown, selected by the selector SIM at this time. Further, the switch relay RIM completes, at the contacts I21, a path, including the contacts I43, for applying direct ground potential to the control wiper CI53, thereby to bring about complete seizure of the connector, not shown, selected at this time; whereupon ground potential in the connector mentioned is returned over the control wiper CI63 in order to complete an alternative .3 holding circuit, including the contacts I21 and I26, for maintaining operated the switch relay RIZI). Further, the switch relay RIZI) completes, at the contacts I21, a path, including the contacts I43 and I44, for short-circuiting the winding of the test relay RI I0, thereby to cause the latter relay to restore. Finally, the switch relay RI2II prepares, at the contacts I28, a path for connecting the EC conductor CIM, extending from the finder FIOU into the selector SIOO, to the EC wiper :11 I64; which connection is not completed at this time, as previously noted, since the set of switch springs SI I2 is not actuated. Upon restoring the hold relay RI40 interrupts, at the contacts I43,

the previously traced original holding circuit, 70 for maintaining operated the switch relay RIZD; whereby the latter relay is maintained in its operated position at this time by virtue of the return of ground potential from the selected connector over the associated trunk to the control till wiper CI63, as previously noted. Also, upon restoring the test relay RI III interrupts, at the contacts N2, the original circuit for operating the switch relay RI 20; which is without effect at this time.

At this time the selector SIllIl has operated to seize and idle one of the connectors, not shown, and has switched the loop circuit extending from the calling subscriber substation A through to the connector mentioned whereby the next two digits dialed at the calling subscriber substation A are effected to bring about operation of the selected connector; all in a conventional manner. After the connection has been set up from the calling subscriber substation. A via the finder FIIJU, the selector SIM and the connector, not shown, to the called subscriber substation, and the connection is ultimately released, the connector mentioned is released; whereby ground potential is removed therein from the control wiper CI63 bringing about the release of the switch relay RIZII in the selector SIIlIl. Upon restoring the switch relay RIZO completes, at the contacts I25, a circuit, including the contacts II I, I32, I42 and I53 and the set of switch springs SI'GS for operating the. release magnet MIBZI; whereby the wiper carriage of the Strowgei' mechanism I6!) is released and returned to its normal position. At this time the sets of switch springs SI69, SI 10 and SI'II are actuated; and, also, the set of switch springs SI'IZ is returned to its normal positionin the event it occupies its operated position. More particularly, the set of switch springs SI69 is actuated, thereby to interrupt the'previouslytraced circuit for operatina the release magnet MI68. Also, the switch relay RIZII recompletes, at the contacts Ill and I23, the connections between the upper and lower windings of the line relay RI30 and the line conductors CI Ill and CI02 extending to the finder FIBB. At this time the selector SIIlIl is completely released and ground potential is removed from the control conductor CIIJ3 extending to the finder FIIlIl; whereby the finder FIIIO is released restoring the set of switch springs S188 to its normal position At this time, the link I30 is completely released and available for further use. When the finder FIIIII is thus released the line circuit 4| is controlled, thereby to mark the subscriber line 40 extending to the subscriber substation A as idle to the connectors in the associated group having access thereto.

In view of the foregoing description of a local call from the calling subscriber substation A via the finder FIOII, the selector SIM and the connector, not shown, to 2. called subscriber substation in the central oillce I0, it will be understood that local calls from the subscriber substations B and C are extended in an identical manner to called subscriber substations in the central ofiice I0. In this connection it is pointed out that the applications of no potential and direct ground potential respectively to the EC conductor CIIM incident to the operations of the finder FIIlll to find the calling lines and respectively extending to the calling subscriber substations B and C, in the two cases, is without effect, since the set of switch springs SI I2 is not operated incident to the extension of local calls via the selector SIIlII from the calling subscriber substations B and C.

Trunk calls from the central oiflce 10 to the distant exchange 20 First, assume that a call has been initiated at the subscriber substation A in the ten-line group rendered non-restricted service in the central oflice that the finder F100 of the link 100 has operated to find the subscriber line 40 extending to the subscriber substation A; that the selector S106 is conditioned to be responsive to the first digit dialed at the calling subscriber substation A; and that the call is to be extended to a called subscriber substation, such, for example, as the subscriber substation D in the distant exchange 20. The subscriber at the calling subscriber substation A proceeds to dial the first digit 2, thereby to bring about operation of the selector S100 in a manner substantially identical to that previously explained; whereupon the wiper carriage of the Strowger mechanism 160 is operated two steps in the vertical direction to select the group of trunks, including the trunk 210, and then opcrates automatically to select an idle trunk in this group. Assuming that the wiper carriage of the Strowger mechanism 160 selects the particular trunk 2111 extending to the trunk circuit 360, the trunk 210 is marked as idle by the application of battery potential upon the control conductor C206 thereof, the battery potential being applied to the control conductor C208 by way of the right-hand winding of the answer relay R310 in the trunk circuit 300. When the wiper carriage of the Strowger mechanism 160 seizes the idle trunk 210, the selector S100 is switched through in the manner previously explained; whereby a loop circuit is completed from the calling subscriber substation A to the line conductors C206 and C201 of the trunk 210; which loop circuit extends by way of the contacts 312 and 314, the windings 381 ad 362 of the repeater 380, and the upper and lower windings of the line relay R360 respectively to battery and ground potentials; whereupon the line relay R360 in the trunk circuit 300 operates. Upon operating the line relay R360 completes, at the contacts 361, an obvious circuit for operating the hold relay R350; and completes, at the contacts 362, a loop circuit including the line conductors C391 and C392 of the trunk line 390, the windings 303 and 334 of the repeater 380 and the left-hand winding of the answer relay R310 extending to the incoming connector 465 in the distant exchange whereby the incoming connector 465 is conditioned to be responsive to the next digit dialed at the calling subscriber substation A. While the left-hand winding of the answer relay R310 in the trunk circuit 300 is energized over the above traced loop circuit including the line conductors of the trunk line 390, the latter relay is not poled to operate. Upon operating the hold relay R350 completes, at the contacts 351, a path, including the contacts 331 and 341, for applyin ground potential in the trunk circuit 300 to the control conductor C208 of the trunk 210, thereby to energize the right-hand winding of the answer relay R310, to maintain the switch relay R120 in the selector S100 in its operated position, and to maintain the finder F100 and the line circuit 41 associated with the calling subscriber line in their operated positions; all in the manner previously explained.

Incident to operation of the wiper carriage 'of the Strowger mechanism 160 in the selector S100 two steps in the vertical direction the set of switch springs S112 was actuated in order to close the contacts 114 thereof. Subsequently, when the switch relay R120 in the selector S100 operated, it completed, at the contacts 128, a connection between the EC conductor C104 and.

the EC wiper 164, since the set of switch springs S112 was previously actuated. Thus, when the selector S is switched through the EC wiper 164 connected to the EC conductor C104 causes resistance ground potential to be applied to the EC conductor C209 of the trunk 210' effecting energization in series of the timer cutoff relay R320 and the release relay R330 in the trunk circuit 300, incident to operation of the hold relay R350 therein. This series circuit extends from ground by way of the resistor 190, the contacts 189 of the set of switch springs S186, the EC conductor C104, the contacts 128, the contacts 114 of the set of switch springs S112, the EC wiper 164, the EC conductor C209 of the trunk 210, the windings of R320 and R330 and the contacts 352 to battery. When this series circuit is completed the timer cutofi relay R320 operates; however, the release relay R330 does not operate since it is of the marginal type. Upon operating the timer cutoff relay R320 interrupts, at the contacts 321, a further point in a circuit traced hereinafter for operating the time release relay R340.

The subscriber at the calling subscriber substation A then proceeds to dial the second and third digits over the previously traced loop circuit including the line relay R360 in the trunk circuit 300; whereby the line relay R360 repeats the impulses of the second and third digits mentioned over the loop circuit including the trunk line 390 to the incoming connector 465 in the distant exchange 20. The incoming connector 465 responds to the two digits mentioned to select the subscriber line 410 extending to the called subscriber substation D therein; whereupon the idle or busy condition of the called subscriber line 410 is tested in a conventional manner. In the event the subscriber line 410 extending to the called subscriber substation D is tested by the incoming connector 465 as being busy, busy tone current is returned therefrom over the trunk line 390 and repeated by the trunk circuit 300 over the loop circuit extending to the calling subscriber substation A. On the other hand, in the event the subscriber line 410 extending to the called subscriber substation D is tested as being idle, the incoming connector 465 operates in order to project ringing current thereover and to return ring-back tone current over the previously traced connection to the calling subscriber substation A. Assuming that the called subscriber substation D is idle at this time, when the subscriber thereat answers the call the incoming connector 465 operates in order to complete a telephone connection between the calling subscriber substation A in the central oflice l0 and the called subscriber substation D in the distant exchange 20 and to effect the reversal of polarity over the line conductors of the trunk line 390. The reversal of polarity of the line conductors of the trunk line 390' poles the lefthand winding of the answer relay R310 in the trunk circuit 300 to operate. Upon operating the answer relay R310 completes, at the contacts 311, an obvious circuit for operating the reverse battery relay R310. Upon operating the reverse battery relay R310 reverses, at the contacts 311, 312, 313 and 314 the polarity of the loop circuit extending between the line relay R360 in the trunk circuit 300 and the calling subscriber substation A; which reversal of polarity over the loop circuit mentioned may be employed for metering purposes in a conventional manner. Also the answer relay R310 completes, at the contacts 313, a path, including the contacts 354, for applying ground potential to the start C011: ductor extending into the timer 385, thereby to initiate operation of the timer 385. 'After a predetermined time interval the timer 385 operates in order to connect the grounded commutator segment of the wheel 386 to the associated stop conductor; thereby to prepare a circuit, include ing the contacts 312 and 353, for operating the time release relay R340. mentioned is not completed by virtue of the operated position of the timer cutoff relay R320. More particularly, the operated timer cutoff relay disables the timer 385 to prevent the release of the established connection, since the calling subscriber substation A involved in the established connection is rendered non-restricted service. Accordingly, the established connection between the calling subscriber substation A in the central ofiice l0 and the called subscriber substation D in the distant exchange persists for any desired time interval at the convenience of the subscribers at the substations mentioned.

At the conclusion of the connection when the subscriber at the called subscriber substation D in the distant exchange 20 replaces the receiver of the telephone instrument thereat upon its associated switchhook, the incoming connector 465 is controlled to bring about the reversal of polarity over the trunk line 390; whereby the left-hand winding of the answer relay R310 in the trunk circuit 300 is poled to restore. Upon restoring the answer relay R310 interrupts, at the contacts 3', the previously mentioned circuit for maintaining operated the reverse battery relay R3 i 0; whereby the latter relay restores effecting the reversal, at the contacts 3| I, 3l2, sit and 3M, of the polarity over the loop circuit extending between the calling subscriber substation A and the line relay R360 in the trunk circuit 3&9. Also, upon restoring the answer relay R319 interrupts, at the contacts 313, the previously mentioned path for applying ground potential to the start conductor extending into the timer 3815; thereby to arrest further operation of the timer 385. This operation has no particular utility in the present example, since the present call was not timed; however, it is useful in another example described hereinafter wherein calls are timed. In other words, the completed connection must persist for a predetermined time interval in order to bring about operation of the timer 205 to effect operation of the time release relay R389 under certain conditions in conjunction with the example mentioned, as explained more fully hereinafter.

When the subscriber at the calling subscriber substation A in the central oflice I0 replaces the receiver of the telephone'instrument thereat upon its associated switch-hook the previously traced loop circuit extending to the line relay R360 in the trunk circuit 300 is interrupted in order to cause the latter relay to restore. Upon restoring the line relay R360 interrupts, at the contacts 362, the previously traced 100p circuit, including the trunk line 390, extending to the incoming selector 465 in the distant exchange 20; whereby the incoming selector 465 is released in order to operate the line circuit 41| associated with the subscriber line 410 bringing about marking of the subscriber line 410 as idle to the connectors of the link-400, etc., hav-' ing access thereto. Also,'the line relay R360 interrupts, at the contacts 36!, the previously mentioned circuit for maintaining operated the However, the circuit hold relay R350; whereby the latter relay restores shortly thereafter, it being of the slow-to-release type. Upon restoring the hold relay R350 interrupts, at the contacts 354, another point in the previously traced path for applying ground potential to the start conductor extending to the timer 315, thereby positively to arrest operation of the timer 385; and interrupts, at the contacts 352, the previously traced series circuit for energizing the windings of the timer cutoff relay R320 and the release relay R330, thereby to cause the timer cutoff relay R320 to restore. Finally, the hold relay R350 interrupts, at the contacts 35!, the previously traced circuit for applying ground potential to the control conductor C208 of the trunk 2 i 0, thereby to deenergize the righthand winding of the answer relay R310; whereby battery potential is applied by way of the righthand Winding of the answer relay R310 to the control conductor C208 of the trunk 2l0. When ground potential is removed from and battery potential is applied to the control conductor C208 of the trunk 2| 0, the trunk H0 and the connected trunk circuit 300 are marked as idle to the selectors of the various links I60, etc., having access thereto. Also, when ground potential is removed from the control conductor C208 of the trunk 2|0, the previously traced circuit for maintaining operated the switch relay Rl20 in the selector S|00 is interrupted; whereupon the latter relay restores eflecting the release of the selector SIM and the finder Fl00 in the manner previously explained. At this time the linl: I00 is completely released and available for further use. When the finder FIIJD is thus released, ground potential is removed from the control conductor of the subscriber line 40; whereby the line circuit 4| is operated in order to marl; the subscriber line 40 extending to the subscriber substation A as idle to the connectors in the associated group having access thereto.

Now assume that a call has been initiated at the subscriber substation B in the ten-line group rendered limited service in the central office [0; that the finder Fl00 of the link I00 has operated to find the subscriber line extending to the subscriber substation B; that the selector Sl00 is conditioned to be responsive to the first digit dialed at the calling subscriber substation B; and that the call is to be extended to a called subscriber substation, such, for example, as the subscriber substation D in the distant exchange 20. The subscriber at the calling subscriber substation B proceeds to dial the first digit 2, thereby to bring about operation of the selector Sl00 to select an idle trunk in the group, including the trunlg 2l0, in the manner previously explained. Assuming that the selector SHED seizes the particulartrunk 2 I 0, the line relay R360 and the hold relay R350 in the trunk circuit 300 are operated, the line relay R360 effecting seizure over the trunk line 390 of the incoming connector 465 in the distant exchange 20; all in the manner previously explained.

In the present example the wiper carriage of the Strowger mechanism H31 in the finder Fl 00 in the link I00 occupies its second vertical step seizing the subscriber line 50 extending to the calling subscriber substation B; whereby the set of switch springs Sl86 is operated in order to cause no potential to be applied to the EC conductor Cl04. Also, the set of switch springs S112 in the selector S|00 is operated, causing no potential to be applied to the EC conductor C209 of the trunk 2l0; whereby neither the timer cutoff relay R320 nor the release relay R330 in the trunk circuit 3% is operated in the present example.

The subscriber at the calling subscriber substation 13 then proceeds to dial the second and third digits; whereby the line relay R360 in the trunk circuit repeats the two digits mentioned over the trunk line 39b in ord-r to bring about operation of the incoming connector 465 to seize the subscriber line 41% extending to the called subscriber substation D in the distant exchange 2 all in the manner previously explained. The operations of the incoming connector 465 to test and to project ringing current over the subscriber line Mt in the event it is idle are the same as previously explained; and when the subscriber at the called subscriber substation D answers the call the incoming connector 465 is operated to bring about the reversal of polarity of the trunk line 3% effecting operation of the answer relay Rtlfi in the trunk circuit 398, as previously explained. Upon operating the answer relay R318 completes, at the contacts 5153,, the previously traced path for applying ground potential to the start conductor extending into the timer 335, thereby to initiate operation of the timer 385. At any time should the subscriber at the called subscriber substation D replace the receiver of the telephone instrument thereat upon its associated switchhook, the incoming connector 455 is controlled to bring about reversal of polarity over the trunk line in order to effect restoration of the answer relay R3?!) in the trunk circuit 300, and the consequent arresting of operation of the timer all in the manner previously explained. Later, should the subscriber at the called subseriber substation D again remove the receiver of the telephone instrument thereat from its associated switchhook, the incoming connector 4:65 is controlled in order, again, to reverse the polarity of the trunk line 39%, thereby to effect reoperation oi the answer relay R316 in the trunk cirouitsbll in order to initiate reoperation of the timer .385.

In the event the established connection between the calling subscriber substation B in the central ofiice it and the called subscriber substation Din the distant exchange 20 persists for a predetermined time interval, complete operation oi the timer 385 takes place; whereby ground potential is applied to the associated stop conductor, thereby to complete a circuit, including the contacts 3E2, 353 and SH for operating the time release relay R349. Upon operating the time release relay R346 interrupts, at the contacts 34!, the previously traced path for applying ground potential to the control conductor C288 of the trunk 2H3 in order to bring about release of the tor sass and the finder EH in the link tilt; all in the manner previously explained. When the link we is thus released, the line circuit 5'! associated with the subscriber line 5! extending to the calling subscriber substation B, is locked out in the event the subscriber at the calling subscriber substation B has not replaced the receiver of the telephone instrument thereat upon its associated switchhook at this time; whereby the subscriber line 50 is marked as busy both to the finders of the links in the first group having access thereto and to the connectors in the associated group having access thereto. Also, when the link 4533 is released :the trunk circuit 3% is released and rendered available for further use; and the incoming connector 465 is released; all in the manner previously explained. When the incoming-connector 4'65 is thus released, the line circuit ll! associated with the subscriber line 410 extending to the called subscriber substation D in distant exchange 20 is locked out in the event the subscriber at the called subscriber substation D has not replaced the receiver of the telephone instrument thereat upon its associated switchhook at this time; whereby the subscriber line till is marked as busy both to the finders and to the connectors of the links F ltil, etc., having access thereto.

Of course, it will be understood that the normal release of the established connection between the call-ing subscriber substation B in the central oiilce it and the called subscriber substation D in the distant exchange .20 takes place in the normal manner when the subscriber at the calling subscriber substation B replaces the receiver of the telephone instrument thereat upon its associated switchhook. In other words, the forced release of the established connection under the control of the timer 385 takes place in the .manner described above only in conjunction with established connections which persist for .a predetermined and abnormally long time interval.

Finally, assume that a call has been initiated at the subscriber substation C in the ten-line group rendered restricted service in the central oITlce l9; that the finder F of the link mil has operated to find the subscriber line 55 extending to the subscriber substation C; that the selector Sill-t is conditioned to be responsive to the first digit dialed at the calling subscriber substation C; and that the subscriber at the calling subscriber substation C attempts the extension of a connection to ;a called subscriber substation in the distant exchange 20. The subscriber at the calling subscriber substation C proceeds to dial the first digit 2, thereby to bring about operation of the selector ,Sifll] to select an idle trunk in the group, including the trunk M5, in the manner previously explained. Assuming that the selector Slllil seizes the particular trunk 259, the line relay R360 and the hold relay R356 in the trunk circuit 300 are operated, the line relay R366 efiecting seizure over the trunk line .399 of the incoming connector 465 in the distant exchange 28; all in the manner previously explained.

In the present example, the wiper carriage of the Strowger mechanism 1:81 in the finder Flea! in :the link H30 occupies its third vertical step seizing the subscriber line 60 extending to the calling subscriber substation C; whereby the set of switch springs S186 is operated in order to cause direct ground potential to be applied to the EC conductor CIM. Also, the set of switch springs SHZ in the selector S100 is operated causing direct ground potential to be applied to the EC conductor C209 of the trunk 2H1; whereby both the timer cutoff relay R320 and the re lease relay R330 in the trunk circuit 359 are operated. The release relay R338 operates in the present example in the previously traced series circuit by virtue of the fact that direct ground potential is applied to the EC conductor case of the trunk 2H], the release relay R339 being of the marginal type. Upon operating the release relay R330 interrupts, at the contacts eat, the previously traced path for applying ground potential to the control conductor 02st of the trunk 2H3; thereby to elTect release of the trunk circuit 3% and the link WE in the manner previously explained. When the trunk circuit 3538 is thus released, the incoming connector in the distant exchange 20 is released; and when the link It!) is thus released, the line circuit ti Trunk calls from the central office 10 to the, remote exchange 30 First, assume that a call has been initiated at the subscriber substation A in the ten-line group rendered non-restricted service in the central ofiice I; that the finder FIDO of the link I00 has operated to find the subscriber line 40 extending to the subscriber substation A; that the selector SI00 is conditioned to be responsive to the first digit dialed at the calling subscriber substation A; and that the call is to be extended to a called subscriber substation in the remote exchange 30. The subscriber at the calling subscriber substation A proceeds to dial the first digit 1, thereby to bring about operation of the selector SI00 in a manner substantially identical to that previously explained; whereupon the Wiper carriage of the Strowger mechanism I60 is operated one step in the vertical direction to select the group of trunks, including the trunk 205, and then operates automatically to select an idle trunk in this group. Assuming that the wiper carriage of the Strowger mechanism I00 selects the particular trunk 205 extending to the secondary trunk 200, the trunk 205 is marked as idle by the application of battery potential upon the control conductor C203 thereof, the battery potential being applied to the control conductor C203 by way of the contacts HI and the resistor 222 in the secondary trunk 20. When the wiper carriage of the Strowger mechanism I 60 seizes the idle trunk 205, the selector SI00 is switched through in the manner previously explained; whereby a loop circuit is completed from the calling subscriber substation A to the line conductors C20! and C202 of the trunk 205; which loop circuit extends by Way of the resistor 2I4 and the contacts 243 and MI and the winding of the line relay R230 respectively to ground and battery potentials; whereupon the line relay R230 in the secondary trunk 200 operates. Upon operating the line relay R230 completes, at the contacts 23I, a path, including the contacts 246 and 22I, for applyin ground potential to the control conductor C203 of the trunk 205, thereby to maintain operated the selector SI00, the finder FI00 and the line circuit 4| associated with the subscriber line 40 extending to the calling subscriber substation A; all in the manner previously explained.

Also, the line relay R230 completes, at the contacts 23I and 232, a path for applying direct ground potential to the upper terminal of the test rela R240; the lower terminal of the test relay R240 being connected by way of the contacts 216 and the magnet M215 of the hunt switch 210 to battery potential. Further, the line relay R230 completes, at the contacts 233, a path, including the contacts 241 and 26I, between the lower terminal of the test relay R240 and the wiper 213 of the hunt switch 210. Assuming that the wipers noted of the hunt switch 210 happen to engage the tenth contacts in the associated contact banks at this time, ground potential appears upon the tenth contact engaged by the wiper 213 of the hunt switch 210; thereby completing a path for short circuiting the winding of the test relay R240 and a direct circuit for operating the magnet M215. The path for short circuiting the winding of the test relay R240 extends from the grounded wiper 213 of the hunt switch 210 by way of the contacts 26I, 241 and 233, the winding of R240 and the contacts 232 and 23I to ground; and the direct circuit for operating the magnet M215 extends from the grounded wiper 213 of the hunt switch 210 by way of the contacts 2SI, 241, 233 and 216 and the magnet M215 to battery. Accordingly, the test relay R240 being short circuited does not oper ate; whereas the magnet M215 operates. Upon operating the magnet M215 interrupts, at the contacts 210, the above traced operating circuit therefor; whereupon the magnet M215 restores to reprepare, at the contacts 216, the above traced circuit for operatin the magnet M215 and to drive the wipers noted of the hunt switch 210 one step in the clockwise direction into engagement with the first contacts in the associated contact banks. At this point, it is noted that the group of seven incoming trunks 280, etc., extending to the group of seven trunk circuits 21I, etc., terminating the group of seven trunk lines 282, etc., extending to the remote exchange 30 are terminated on the first seven contacts in the contact bank of the hunt switch 210; whereas the group of three incoming trunks 200, etc., extending to the group of three trunk circuits 29I, etc., terminating the group of three trunks 202, etc., extending to the operator switchboard 295 are terminated on the last three contacts in the contact bank of the hunt switch 210; the hunt switch 210 being of the ten-point rotary type, as previously noted.

When the wipers noted of the hunt switch 210 engaged the first contacts in the associated contact bank, the first incoming trunk in the group of seven, including the incoming trunk 280, is selected and this trunk is tested. In the event the trunk mentioned is busy at this time, ground potential appears upon the control conductor thereof applying ground potential to the wiper 213 of the hunt switch 210; whereby the winding of the test relay R240 is again short-circuited and the magnet M215 is reoperated. On the other hand, in the event the trunk mentioned is idle at this time, battery potential appearing upon the control conductor thereof completes a path substantially identical to that previously traced for short circuiting the magnet M215; whereupon a circuit, including the contacts 23I, 232 and 216, is completed for energizing the winding of the test relay R240 in series with the magnet M215; and a multiple circuit, including the contacts 23I, 232, 233, 241 and 26L the wiper 213 of the hunt switch 210 and the control conductor of the trunk mentioned is completed for energizing the winding of the test relay R240 from battery potential appearing in the trunk circuit terminating the trunk mentioned. When the circuits mentioned are completed the test relay R240 operates shortly thereafter, it being of the slowto-operate type. Assuming that all of the incoming trunks in the group, including the incoming trunk 280, and preceding the incoming trunk 280, are busy; and. that the incoming trunk 280 is idle; the magnet M215 operates buzzer-fashion to drive the wipers noted into engagement with the contacts in the associated contact banks terminating the incoming trunk 280. Since it is assumed that the incoming trunk 280 is idle at this time, batter potential appears upon the control conductor thereof effecting short-circuiting of the magnet M215 and energization of the test relay R240; whereupon the test relay R240 operates shortly thereafter as previously noted. Upon operating the test relay R240 interrupts, at the contacts 2411, the previously traced path for short circuiting the magnet M275; and completes, at the contacts 248, a path, including the contacts 23!, 232 and 28!, for applying direct ground potential to the wiper 213 of the hunt switch 210; whereby the trunk circuit 28 l, associated with the incoming trunk 280, is seized bringing about the application of ground potential therein to the control conductor of the incoming trunk 280, and consequently to the wiper 213 of the hunt switch 270 in order to complete a holding circuit substantially identical to that previously traced for energizing the winding of the test relay R240 in series with the magnet M2275. When this holding circuit is completed the test relay R240 is maintained in its operated position; however, the magnet M225 does not operate due to the high series resistance of the winding of the test relay R240. Also, the test relay R240 completes, at the contacts 2E5, a path, including the contacts 22l and for connecting the control conductor C203 of the trunk 205 to the grounded wiper 213 of the hunt switch 210, thereby to maintain operated the selector S100, the finder Fl 00 and the 1 Finally, the test relay R240 completes, at the contacts 202 and 244, an alternative loop circuit extending from the calling subscriber substation A to the wipers 2H and 212 of the hunt switch 210 and then to the line conductors of the incoming trunk 280; which loop circuit is completed in the trunk circuit 23l in order to bring about complete seizure of the trunk circuit 28l in the manner previously explained; whereby the trunk line 282 extending to the remote exchange is seized in order to condition the automatic switching apparatus therein to be responsive to the following digits dialed at the calling subscriber substation A.

Incident to operation of the wiper carriage of the Strowger mechanism I in the selector SE00 one step in the vertical direction, the set of switch springs SllZ was actuated in order to close the contacts H4 thereof. Subsequently, when the switch relay RI20 in the selector S|00 operated it completed, at the contacts I28, a connection between the EC conductor Cl04 and the EC wiper I54, since the set of switch springs SI12 was previously actuated. Thus, when the selector Sl00 is switched through, the EC wiper I64 connected to the EC conductor Cl04 causes resistance ground potential to be applied to the EC conductor C204 of the trunk 205 efiecting energization in series of the timer cutofi relay R250 and the intercept rela R260 in the secondary trunk 200. This series circuit extends from ground by way of the resistor I 90, the contacts I89 of the set of switch springs S l 85, the EC conductor Clfl l, the contacts I28. the contacts I14 of the set of switch springs 8H2, the EC wiper I64, the EC conductor C204 of the trunk 205 and the windings of R250 and R260 to battery. When this series 22 circuit is completed the timer cutofi relay R250 operates; however, the intercept relay R260 does not operate, since it is of the marginal type. Upon operating the timer cutoff relay R250 interrupts, at the contacts 25l, a further point in a circuit traced hereinafter for operating the time release relay R220.

The subscriber at the calling subscriber substation A then proceeds to dial the remainder of the digits over the previously traced loop circuit into the trunk circuit 28I; which digits are repeated thereby over the trunk line 282 into the switching apparatus in the remote exchange 30 in order to cause the subscriber line extending to the called subscriber substation in the remote exchange 30 to be seized and tested in a conventional manner. Assuming that the subscriber substation in the remote exchange 30 is idle at this time, the associated switching apparatus operates in order to cause ringing current to be projected thereover and ring-back tone current to be returned over the trunk line 282 to the trunk circuit 28l and thence repeated over the previously traced loop circuit to the calling subscriber substation A in the central oflice i0. Subsequently, when the subscriber at the called subscriber substation in the remote exchange 30 answers the call the associated switching apparatus operates in order to reverse the polarity over the trunk line 282 effecting operation of the answer relay in the trunk circuit 205 and the consequent reversal of polarity over the loop circuit extending to the calling subscriber substation A in the central office Hi. When the polarity of the loop circuit extending to the calling subscriber substation A is thus reversed, the unidirectional current conducting device, or copper oxide rectifier 21s shunting the righthand winding of the answer relay R2l0 in the secondary trunk 200 blocks the passage of current therethrough; whereby the current is diverted through the right-hand winding of the answer relay RZHJ eiiecting operation thereof. Upon operating the answer relay R2l0 completes, at the contacts 2! l, a holding circuit for energizing the left-hand winding of the answer relay R2l0 and including the grounded control conductor 0203- of the trunk 205. Also, the answer relay R250 completes, at the contacts 242, an obvious path for applying ground potential to the start conductor extending to the timer 2E5, thereby to initiate operation of the timer 2i5. After a predetermined time interval the timer 25.5 operates in order to connect the grounded commutator segment of the wheel 2|5 to the associated stop conductor, thereby to prepare a circuit for operating the time release relay R220. However, the circuit mentioned is not completed by virtue of the operation of the timer cutoff relay R250. More particularly, the operated timer cutoff relay R250 disables the timer 255 to prevent the release of the established connection, since the calling subscriber substation A involved in the established connection is rendered non-restricted service. Accordingly, the established connection between the calling subscriber substation A in the central ofiice l0 and the called subscriber substation in the remote exchange 30 persists for any desired time interval at the convenience of the subscribers at the substations mentioned.

At the conclusion of the connection when the subscriber at the called subscriber substation in the remote exchange 30 replaces the receiver of the telephone instrument thereat upon its associated switchhook, the associated switching apparatus is controlled to bring about the reversal of polarity over the trunk line 282; whereby the trunk circuit 231 reverses the polarity over the associated incoming trunk 280 and the loop circuit extending to the calling subscriber substation A in the central office whereupon the copper oxide rectifier 213 again shunts the righthand winding of the answer relay R210 in the secondary trunk 2110. However, the answer relay R210 remains in its operated position by virtue of the completed holding circuit for energizing the left-hand winding thereof. When the subscriber at the calling subscriber substation A in the central office 10 replaces the receiver of the telephone instrument thereat upon its associated switchhook, the previously traced loop circuit extending to the trunk circuit 281 is interrupted in order to cause ground potential to be removed from the control conductor of the incoming trunk 280, bringing about the restoration of the test relay R240 in the secondary trunk 200. Upon restoring the test relay R240 interrupts, at the contacts 245, a further point in the previously traced path, including the control wiper 213 of the hunt switch 210, for applying ground potential to the control conductor C203 of the trunk 205; whereby the selector S100 and the finder F100 are released in the manner previously explained. When the finder F100 is thus released, ground potential is removed from the control conductor of the subscriber line 40; whereby the line circuit 41 is operated in order to mark the subscriber line 40 extending to the subscriber substation A as idle to the connectors in the associated group having access thereto. Also, when the selector S100 is released, the previously traced circuit for applying resistance ground potential to the EC conductor C204 of the trunk 205 is interrupted effecting the restoration of the timer cutoff relay R250 in the secondary trunk 200. Also, when ground potential is removed from the control conductor C203 of the trunk 205, the previously traced holding circuit for energizing the left-hand winding of the answer relay R210 in the secondary trunk 200 is interrupted in order to cause the latter relay to restore. Upon restoring the answer relay R210 interrupts, at the contacts 212, the previously mentioned path for applying ground potential to the start conductor extending into the timer 215; thereby to arrest operation of the timer 215. At this time, the secondary trunk circuit 200 is completely released and battery potential is applied by way of the resistor 222 and the contacts 221 to the control conductor C203 of the trunk 205, thereby to mark the trunk 205 as idle to the selectors in the various groups having access thereto. It is noted that the hunt switch 210 is not of the homing type; whereby the wipers noted thereof remain operated to the last operated position selecting the incoming trunk 280 extending to the trunk circuit 281.

Also, when the loop circuit extending from the calling subscriber substation A in the central ofiice 10 to the trunk circuit 281 is interrupted, the trunk circuit 281 is released; whereby battery potential is applied to the control conductor of the incoming trunk 280 in order to mark the incoming trunk 280 as idle to the hunt switches in the various secondary trunks having access thereto. Further, the trunk circuit 281 opens the loop circuit extending over the trunk line 282 to the switching apparatus in the remote exchange 30, thereby to bring about the release of the switching apparatus mentioned and the consequent operation of the line circuit associated with the called subscriber line therein in order to mark this subscriber line as idle to the associated switching apparatus having access thereto. I

Now, assume that a call has been initiated at the subscriber substation B in the ten-line group rendered limited service in the central ofiice 10; that the finder F of the link 100 has operated to find the subscriber line 50 extending to the subscriber substation B; that the selector S100 is conditioned to be responsive to the first digit dialed at the calling subscriber substation B; and that the call is to be extended to a called subscriber substation in the remote exchange 30. The subscriber at the calling subscriber substation B proceeds to dial the first digit 1, thereby to bring about operation of the selector S100 to select an idle trunk in the group, including the trunk 205, in the manner previously explained. Assuming that the selector S100 seizes the particular trunk 205, the line relay R230 in the secondary trunk 200 operates in order to initiate operation of the magnet M215 in conjunction with operation of the test relay R240; whereby the hunt switch 210 is controlled to select an idle incoming trunk in the group, including the incoming trunk 280 extending to an idle trunk circuit in the group including the trunk circuit 281. Assuming that the trunk circuit 281 is idle at this time, the incoming trunk 280 individual thereto is marked as idle by the application oi battery potential upon the control conductor thereof; whereupon the test relay R240 may operate immediately prior to operation of the magnet M215 in the event the wipers noted of the hunt switch 210 engaged the sixth contacts in the associated contact bank terminating the incoming trunk 280. In any case, the magnet M215 operates in conjunction with the test relay R240 in order to bring about operation of the hunt switch 210 to select an idle incoming trunk in the group mentioned extending to an idle trunk circuit. Assuming that the hunt switch 210 selects the incoming trunk 280 extending to the trunk circuit 281, the test relay R240 operates in order to arrest further operation of the magnet M215; all in the manner previously explained. Further, the test relay R240, upon operating, efiects holding of the selector S100, the finder F100 and the line circuit 51 in their operated positions in the manner previously explained. Also, the test relay R240 brings about the restoration of the line relay R230 shortly after operation of the test relay R240; whereupon a loop circuit is completed between the calling subscriber substation B and the trunk circuit 281. The trunk circuit 281 operates in order to bring about seizure over the trunk line 282 of the switching apparatus in the remote exchange 30; all in the manner previously explained.

In the present example the wiper carriage of the Strowger mechanism 181 in the finder F100 in the link 100 occupies its second vertical step seizing the subscriber line 50 extending to the calling subscriber substation B; whereby the set of switch springs S101 is operated in order to cause no potential to be applied to the EC conductor C104. Also, the set of switch springs S112 in the selector S100 is operated causing no potential to be applied to the EC conductor C204 25 of the trunk 205; whereby neither the timer cutoff relay R250 nor the intercept relay R260 is operated in the present example.

The subscriber at the calling subscriber substation B then proceeds to dial the following digits; whereby the trunk circuit 28l operates in order to repeat the digits mentioned over the trunk line 282 to the switch apparatus in the remote exchange 38 effecting operation thereof to seize the subscriber line extending to the called subscriber substation therein. The operations of the switching apparatus in the remote exchange 30 to test and to project ringing current over the subscriber line extending to the called subscriber substation, in the event it is idle, are the same as previously explained; and when the subscriber at the called subscriber substation in the remote exchange 30 answers the call the associated switching apparatus operates in order to reverse the polarity over the trunk line 282 causing the trunk circuit 28! to operate and reverse the polarity over the loop circuit extending to the calling subscriber substation B in the central ofiice Hi. When the polarity of the loop circuit extending to the calling subscriber substation B and the trunk circuit 28! is reversed, the copper oxide rectifier 2l3 blocks the passage of current therethrough effecting energization of the right-hand winding of the answer relay R210 in the trunk circuit 200 in the manner previously explained; whereupon the answer relay R2) operates completing, at the contacts 2| l, the previously traced holding circuit, including the grounded control conductor 0283 of the trunk 205, for energizing the lefthand winding thereof, and initiating operation of the timer 2I5. At this time an established connection is completed between the calling subscriber substation A in the central ofiice l9 and the called subscriber substation in the remote exchange 30. At any time should the subscriber at the called subscriber substation in the remote exchange 3!] replace the receiver of the telephone instrument thereat upon its associated switchhook, the associated switching ap paratus operates in order to reverse the polarity over the trunk line 282 causing the trunk circuit 28! to reverse the polarity over the loop circuit extending to the calling subscriber substation B. This operation is without effect, however, to control the answer relay RZIG, since a direct holding circuit is completed for the left-hand winding thereof, including the contacts 2!! and the grounded control conductor C203 of the trunk line 205. timer 2l5 continues until the subscriber at the calling subscriber substation B in the central oiiice I replaces the receiver of the telephone instrument thereat upon its associated switchhook in order to efiect release of the equipment involved in a manner more fully explained hereinafter.

In the event the established connection between the calling subscriber substation B in the central office Ill and the called subscriber substation in the remote exchange 3 3 persists for a predetermined time interval, complete operation or" the timer'2l5 takes place; whereby grouncl potential is applied to the associated stop conduct-or, thereby to complete a circuit, including the contacts for operating the time release relay R226. Upon operating the time release relay 322i} interrupts, at the contacts Hi, the previously traced path for applying ground potential to the control conductor C293 of the trunk 285 in order to bring Accordingly, operation of the about the release of the selector Slllfl and the finder Fill!) in the link me; all in the manner previously explained. When the link Hill is thus released, the line circuit 5!, associated with the subscriber line 50 extending to the calling subscriber substation B, is locked out in the event the subscriber at the calling subscriber substation B has not replaced the receiver of the telephone instrument thereat upon its associated switchhook at this time; whereby the subscriber line 50 is marked as busy both to the finders of the links in the first group having access thereto and to the connectors in the associated group having access thereto. Also, when the link Hill is released the secondary trunk 2% is released and rendered available for further use; and the trunk circuit 285 is released and rendered available for further use; all in the manner previously explained. When the trunk circuit 28l is released, the loop circuit extending therefrom by way of the trunk line 282 to the switching apparatus in the remote exchange 38 is opened, efiecting release of the switching apparatus mentioned; whereby the line circuit, associated with the subscriber line extending to the called subscriber substation in the remote exchange 30, is locked out in the event the subscriber at the called subscriber substation mentioned has not replaced the receiver of the telephone instrument thereat upon its associated switchhook at I this time; whereby the subscriber line extending to the called subscriber substation mentioned is marked as busy to the switching apparatus having access thereto.

Of course, it will be understood that the normal release of the established connection between the calling subscriber substation B in the central oflice ill and the called subscriber substation in the remote exchange 39 takes place in the normal manner when the subscriber at the calling subscriber substation B replaces the receiver of the telephone instrument thereat upon its associated switchhook. In other words, the forced release of the established connection under the control of the timer 2.!5 takes place in the manner described above only in conjunction with established connections which persist for a predetermined and abnormallylong time.

Finally, assume that a call has been initiated at the subscriber substation C in the ten-line group rendered restricted service in the central office l0; that the finder Flflll of the link ill!) has operated to find the subscriber line 65 extending to the subscriber substation C; that the selector sum is conditioned to be responsive to the first digit dialed at the-calling subscriber substation C; and that the subscriberat the calling subscriber substation C attempts the extension of a connection to a called subscriber substation in the remote exchange 39. The subscriber at the calling subscriber substation C proceeds to dial the first digit 1; thereby to bring about operation of the selector SI iii! to select an idle trunk in the group, including the trunk 29-5, in the manner previously explained. Assuming that the selector S l Bil seizes the particular trunk 2B5, the line relay B23!) in the secondary trunk 20!] is operated in the manner previously explained.

In the present example, the wiper carriage of the Strowger mechanism H3! in the finder Flllll in the link Hill occupies its third vertical step seizing the subscriber line fill extending to the calling subscriber substation C; whereby the set of switch springs SlBi is operated in order to cause direct ground potential to be applied to the EC conductor Cl04. Also, the set of switch springs Sl12 in the selector S! is operated causing direct ground potential to be applied to the EC conductor C204 of the trunk 205; whereby both the timer cutoff relay R250 and the intercept relay R260 in the secondary trunk 200 are operated. The intercept relay R260 operates in the present example in the previously traced series circuit by virtue of the fact that direct ground potential is applied to the EC conductor C204 of the trunk 205, the intercept relay R260 being of the marginal type. Upon operating the timer cutofi relay R250 interrupts, at the contacts 25!, a further point in the previously traced circuit for operating the time release relay R220; thereby to prevent operation of the latter relay in the present example. Upon operating the intercept relay R260 interrupts, at the contacts 25 l, the normally completed connection between the control wiper 213 of the hunt switch 210 and the lower terminal of the test relay R240; and completes, at the contacts 262, a connection, including the contacts 241 and 233, between the control wiper 214 of the hunt switch 210 and the lower terminal of the test relay R240. In the present case, the first seven contacts in the contact bank, associated with the control wiper 214 of the hunt switch 210, are connected directly to ground potential, thereby to short-circuit the winding of the test relay R240 and to cause intermittent operation of the magnet M215 in the manner previously explained; whereby the wipers noted of the hunt switch 210 are driven into engagement with the eighth contacts in the associated contact banks. When the control wipers 214 of the hunt switch 210 engage the eighth contacts in the associated contact bank, the first incoming trunk in the group of three, including the incoming trunk 290, is tested by the test relay R240. Assuming that the first trunk mentioned is busy, the winding of the test relay R240 is again shortcircuited and the magnet M215 is reoperated; whereby the wipers noted of the hunt switch 210 are driven into engagement with the ninth contacts in the associated contact banks terminating the incoming trunk 290 extending to the trunk circuit 29!. Assuming that the incomin trunk 290 is idle at this time, battery potential appearing upon the control conductor thereof completes a path substantially identical to that previously traced for short-circuiting the magnet M215; and completes one of the two previously mentioned multiple circuits for energizing the winding of the test relay R240. Accordingly, the test relay R240 operates to arrest further operation of the magnet M215, to effect restoration of the line relay R230 shortly thereafter, since it is of the slow-to-release type, and to switch the loop circuit extending from the calling subscriber substation through the hunt switch 210 onto the incoming trunk 290; whereby the loop circuit mentioned is recompleted in the associated trunk cir cuit 29!. The trunk circuit 29! then operates to return ground potential over the control conductor of the incoming trunk 290, thereby to maintain operated the test relay R240 in the secondary trunk 200; whereby the selector Sl00, the finder Fl 00 and the line circuit 6! associated with the subscriber line 60 extending to the calling subscriber substation C are maintained in their operated positions for the purpose previously explained. Further, the trunk circuit 29! operates to close the trunk 292 extending to the operator switchboard 295 in order to indicate to the operator thereat that a call is on the trunk 292 Waiting to be answered. Whenthe operator at the switchboard 295 answers the call on the trunk 292, a telephone connection is established to the calling subscriber substation C, and the subscriber thereat is advised that the call has been intercepted since calls from the subscriber substation C to the remote exchange 30 may not be set up directly by the subscriber at the calling subscriber substation C. The operator at the switchboard 295 may undertake the extension of the connection to the desired called subscriber substation in the remote exchange 30 or she may advise the subscriber at the calling subscriber substation C to release the present connection and initiate a direct call to a toll switchboard, not shown, provided in the central office 50.

Subsequently, at the conclusion of the connection the operator withdraws from the trunk 292 and later, when the subscriber at the calling subscriber substation C replaces the receiver of the telephone instrument thereat upon its associated switchhook, the loop circuit extending from the calling subscriber substation C to the trunk circuit 29! is interrupted; whereby the trunk circuit 20! operates to release the trunk 202, and to interrupt the application of ground potential to, and to return battery potential upon, the control conductor of the incoming trunk 290. When ground potential is removed from the control conductor of the incoming trunk 290, the previously traced circuit for maintaining operated the test relay R240 in the secondary trunk 200 is interrupted, causing the latter relay to restore effecting the release of the secondary trunk 200, the selector SWO and the finder F|00 in the manner previously explained. When the finder F is thus released the line circuit 6! is controlled to mark the subscriber line 60 extending to the subscriber substation C as idle to the connectors in the associated group having access thereto.

Operation of the finders in the distant exchange 20 First, assuming that a call is initiated at a subscriber substation, such, for example, as the subscriber substation D in the ten-line group normally rendered non-restricted service in the distant exchange 20; the line circuit 41! is controlled over the associated subscriber line 410 and operates in order to place ground potential upon the start conductor C49! extending to the distributor 490 and to mark the particular rotary position of the contact sets terminating the sub scriber line 410 in the contact banks of the Strowger mechanisms incorporated in the finders of the links in the group. The distributor 490 then operates in order to assign an idle one of the links in the group to find the calling line, such, for example, as the link 400. Also, the distributor 490 marks to the finder F400 of the link 400 the level of the contact set in the contact bank 485 of the Strowger mechanism 48! terminating the calling subscriber line 490; the first level in the present example. The finder F400 is then controlled by the distributor 490; whereby the wiper carriage of the Strowger mechanism 48! is driven one step in the vertical direction and then operated automatically in the rotary direction in search of the calling subscriber line 410.

When the wiper set of the Strowger mechanism 48! engages the tenth contact set in the first level in the contact bank 486 terminating the calling subscriber line 410, further operation thereof is arrested; the distributor 490 eifects operation of the switch through relay R4 0 in the finder F400 and is then released; and the line circuit 41!, associated with the calling subscriber line 470, is controlled in order to mark the subscriber line 470 as busy to the connectors of the link in the group having access thereto. Upon operating the switch through relay R410 completes, at the contacts M5, a holding circuit, not shown, for maintaining it operated; and completes, at the contacts 4H and M2, a loop circuit, including the line wipers 4232 and 483, extending to the calling subscriber substation D; which 100p circuit is completed in the connector C400 to battery and ground potentials, and further includes the contacts 455 and 452, as well as the resistor 435 and the shunting unidirectional current conducting device, or copper oxide rectifier 434. It is noted that the right-hand winding of the answer relay R430 is bridged across the copper oxide rectifier 434' and is shunted thereby, at the present time, in order to prevent operation of the answer relay R430. Also, ground potential in the connector 04% is applied by way of the contacts 453 and M3 to the control Wiper 404, thereby to maintain operated the finder F400 and the line circuit 41! as previously noted.

Also, incident to operation of the finder F400 to find the calling line subscriber line 410, the wiper shaft 488 actuates the set of switch springs S48! to close the contacts 430. whereby no potential is applied to the EC wiper 485 connected by Way of the contacts l to the service relay R420; by virtue of the fact that the calling subscriber line H is terminated in the first level of the contact bank 4% of the Strowger mechanism 48!. Also, the EC contactof the contact set terminating the subscriber line 410 extending to the calling subscriber substation D has no ground potential appearing thereon; whereby no potential in the contact bank 485 of the Strowger mechanism 33i is applied directly to the EC wiper 405. Hence, in the present example, the service relay R liil in the finder F400 is not operated, since the calling subscriber substation D is included in a ten-line group normally rendered non-restricted service and comprises an individual line in this group which is rendered non-restricted service. The failure of the service relay R420 to be operated at this time prevents timing of a connection, ultimately completed by way of the link 400, as explained more fully hereinaiter. I

Now, assuming that a call is initiated at a subscriber substation, such, for example, as the subscriber substation E in the ten-line group rendered limited service in the distant exchange 20; the line circuit lid is controlled over the associated subscriber line M and operates in order to place ground potential upon the start conductor C49i extending to the distributor 490 and to mark the particular rotary position of the contact sets terminating the subscriber line 4'55 in the contact banks of the Strowger mechanism incorporated in the finders of the links in the group. The distributor $95! then operates in order to assign an idle one of the links in the group to find the calling line, such, forexampie, as the link 4%. Also, the distributor 5963 marks to the finder of the link 400 the level of the contact set in the contact bank 4555 of the Strowger mechanism #38! terminating the calling subscriber line 4%; the second level in the present example. The finder F lw is then controlled by the distributor 5.00; whereby the wiper carriage of the Strowger mechanism is driven two steps '30 in the vertical direction and then operated automatically in the rotary direction in search of the calling subscriber line 475.

When the wiper set of the Strowgermechanism 48! engages the second contact set in the second level in the contact bank 485 terminating the calling subscriber line 415 further operation thereof is arrested; the distributor 490 then operates the switch through relay PAW and is released; and the line circuit 416, associated with the calling subscriber line 475, is controlled in order to mark the subscriber line 415 as busy to the connectors of the links in the group having access thereto. Also, at this time, a loop circuit is completed between the calling subscriber substation E and the connector C400; and the answer relay R 430 is not operated; all in the manner previously described. Also, the connector C400 maintains operated the finder F400 and the line circuit 315, as previously noted.

Also, incident to operation of the finder F400 to find the calling subscriber line 415, the wiper carriage shaft 488 actuates the set of switch springs S487 to close the associated contacts 489; whereby direct ground potential is applied to the EC wiper 485 in order to complete a circuit, including the contacts 4 M, for operating the service relay R420. The operation of the service relay R420 in the finder F 500 causes a connection, ultimately completed by way of the link 400, to be timed under the control of the interceptor 445 and the timer switch 440, as explained more fully hereinafter.

Finally, assuming that a call is initiated at. a subscriber substation, such, for example, as the subscriber substation F in the ten-line group rendered non-restricted service, but which individual subscriber substation is rendered restricted service, in the distant exchange 20; the line circuit 48| is controlled over the associated subscriber line 480 and operates in order to place ground potential upon the start conductor C49| extending to the distributor 90 and to mark the particular rotary position of the contact sets terminating the subscriber line 430 in the contact banks of the Strowger mechanisms incorporated in the finders of the links in the group. The distributor 400 then operates in order to assign an idle one or the links in the group to find the calling line, such, for example, as the link 400. Also, the distributor 4% marks to the finder F400 of the link the level of the contact set in the contact bank 436 of the Strowger mechanism 48! terminating the calling subscriber line 490; the first level in the present example. The finder F400 is then controlled by the distributor 490; whereby the wiper carriage of the Strowger mechanism 4% is driven one step in the vertical direction and then operated automatically in the rotary direction in search of the calling subscriber line 480.

When the Wiper set of the Strowger mechanism 48l engages the ninth contact set in the first level in the contact bank 48! terminating the calling subscriber line 480, further operation thereof is arrested; the distributor 490 effects operation of the switch through relay R460 and is released; and the line circuit 48!, associated with the calling subscriber line 480, is controlled in order to mark the subscriber line 48% as busy to the connectors of the links in the group having access thereto. Also, at this time, a loop circuit is completed between the calling subscriber substation F and the connector C400; however,

31 the answer relay R430 is not operated; all as previously explained.

Also, incident to operation of the finder F400 to find the calling subscriber line 481, the wiper carriage shaft 488 actuates the set of switch springs S481 to close the associated contacts 489'; whereby no potential is applied. thereat to the EC wiper 485. However, in the present example, the EC wiper 485 engaged directly the grounded EC contact of the contact set in the contact bank 486 of the Strowger mechanism 481 terminating the subscriber line 480 extending to the calling subscriber substation F; whereby direct ground potential appearing upon the EC wiper 485 completes the previously mentioned circuit, including the contacts 414, for operating the service relay R420 in the finder F400. The operation of the service relay R420 in the finder F400 causes a connection, ultimately completed by way of the link 400, to be timed under the control of the interrupter 445 and the timer switch 440 as explained more fully hereinafter.

Completion of connections in the distant exchange First, assume that a call has been initiated at the subscriber substation D in the ten-line group normally rendered non-restricted service in the distant exchange 20 that the finder F400 of the link 400 has operated to find the subscriber line 410 extending to the subscriber substation D; that the connector C400 is'conditioned to be responsive to the first digit dialed at the calling subscriber substation D; and that the call is to be extended to a called subscriber substation, such, for example, as the subscriber substation E in the distant exchange 20. The subscriber at the calling subscriber substation D proceeds to dial the two digits comprising the directory number of the called subscriber substation E; whereupon the connector C400 operates to seize the subscriber line 415 extending to the called subscriber substation E. The connector C400 then tests the idle or busy condition of the called subscriber line 415, returning busy tone current to the calling subscriber substation D in the event the called subscriber substation E is busy at this time, and projecting ringing current over the called subscriber line 415 and returning ring back current over the calling subscriber line 410 in the event the called subscriber substation E is idle at this time. Assuming that the called subscriber substation E is idle at this time, when the call is answered thereat the connector C400 operates to complete a telephone connection between the calling subscriber substation D and the called subscriber substation E, and to efiect the reversal of polarity over the loop circuit extending to the calling subscriber substation D. When the polarity of the loop circuit extending to the calling subscriber substation D is thus reversed, the copper oxide rectifier 434 blocks the passage of current therethrough; whereby the right-hand winding of the answer relay R430 in the finder F400 is energized. The answer relay R430 operates to complete, at the contacts 431, a holding circuit for energizing the lefthand winding thereof; and to prepare, at the contacts 432, a circuit for energizing the rotary magnet M442 of the timer 440 from the interrupter 445; which circuit is not completed at this time by virtue of the fact that the service relay R420 is not operated, since the Wiper carriage of the Strowger mechanism 481 occupies its first vertical step selecting the subscriber line 410 extending to the calling subscriber substation D closing the contacts 489 and placing no potential upon the EC wiper 485.

More particularly, the restored service relay R420 disables the timer switch 440 to prevent the release of the established connection, since the callin subscriber substation D involved in the established connection is rendered nonrestricted service. Accordingly, the established connection between the calling subscriber substation D and the called subscriber substation E persists for any desired time interval at the convenience of the subscribers at the substations mentioned. At the conclusion of the connection when the subscriber at the called subscriber substation E replaces the receiver of the telephone instrument thereat upon its associated switchhook, the connector C400 operates to efiect the reversal of polarity over the loop circuit extending to the calling subscriber substation D; which operation is without effect, since the answer relay R430 is retained in its operated position by the completed holding circuit for energizing the left-hand winding thereof. When the subscriber at the calling subscriber substation D replaces the receiver of the telephone instrument thereat upon its associated switchhook, the previously traced loop circuit extending to the connector C400 is interrupted; whereby the connector C400 is released interrupting the application of ground potential upon the control wiper C484 causing the finder F400 to be released; whereupon the switch through relay R410 and the answer relay R430 are restored. When the connector C400 is thus released, the line circuit 416 is operated to mark the subscriber line 415 extending to the called subscriber substation E as idle to the connectors C400, etc., having access thereto; and when the finder F400 is released, the line circuit 411 is operated in order to mark the subscriber line 410 extending to the calling subscriber substation D as idle to the connectors C400 etc., having access thereto.

Now assume that a call has been initiated at the subscriber substation E in the ten-line group rendered limited service in the distant exchange 20; that the finder F400 of the link 400 has operated to find the subscriber line 415 extending to the subscriber substation E; that the connector C400 is conditioned to be responsive to the first digit dialed at the calling subscriber substation E; and that the call is to be extended to a called subscriber substation such, for example, as the subscriber substation D in the distant exchange 20. The subscriber at the calling subscriber substation E proceeds to dial the two digits comprising the directory number of the called subscriber substation D, thereby to bring about operation of the connector C400 to seize the subscriber line 410, to test the idle or busy condition of the called subscriber line 410, to return busy tone current or to project ringing current and to return ring-back tone current, under the various conditions in a conventional manner. When the subscriber at the called subscriber substation D answers the call the connector C400 switches through in order to bring about operation of the answer relay R430 in the finder F400 in the manner previously explained.

In the present example the Wiper carriage of the Strowger mechanism 481 in the finder F000 in the link 400 occupies its second vertical step seizing the subscriber line 415 extending to the calling subscriber substation E; whereby the set of switch springs S481 is operated in order to close 

